Between 21 September 1959 and 21 December 1961, 9,006 consecutive pregnancies and births at the University Hospital in Copenhagen, Denmark were intensively studied and recorded as part of a perinatal research project. It is the goal of this project to assess what importance the circumstances of these pregnancies and births (in interaction with genetic and social factors) have in the etiology of subsequent antisocial behavior in these children. We intend to implement these goals by: a) longitudinally following this cohort, noting the incidence and seriousness of delinquent behavior and relating this back to the perinatal information; b) intensively examining a subsample of this cohort which is at high risk for antisocial behavior and describing characteristics differentiating them from low-risk subjects. We will also follow these high-risk subjects, observe which of them evidence antisocial behavior, and describe premorbid characteristics which differentiate the eventually antisocial from the eventually law-abiding subjects. Results to date suggest that a genetic factor is involved in criminality. Twin and family studies have not permitted us to reject the hypothesis that certain autonomic nervous system factors may be part of what is genetically transmitted.